Noise Sources of Lean Premixed Flames

Abstract

The thermoacoustic sound generation mechanisms of lean premixed laminar and turbulent flames are investigated by a two-step approach. First, the conservation equations of a reacting compressible fluid are solved. This solution is used to determine the acoustic source terms of the acoustic perturbation equations (APE). Second, the contributions of the different source terms to the amplitude and phase of the acoustic pressure signal are analyzed by solving the APE in a computational aeroacoustics (CAA) simulation. The results show that it is not sufficient to only consider the unsteady heat release rate fluctuations which occur in the substantial pressure-density relation. The acceleration of density gradients occurring at the flame front is a significant contributor to the overall sound emission. For the investigated laminar and turbulent flames the amplitude and phase of the acoustic pressure signal can only be predicted accurately if both source terms are included in the acoustic analysis.